A light-emitting diode disclosed in GB 1 423 013 has its semiconductor chip embedded in transparent resins by the use of a transfer molding process. Among other things, the possibility of potting the chip with silicone resin is mentioned there.
The production of optical elements from silicone resins for contact lenses is disclosed in U.S. Pat. No. 4,198,131. Enhanced wearer comfort due to the use of silicone resins is emphasized there.
The use of various silicone resins having a viscosity less than one pascal-second in conjunction with light-emitting diodes is disclosed in EP 1 424 363 A1.
WO 01/50540 A1 discloses a surface-mountable light-emitting diode source wherein a radiation-emitting semiconductor chip on a leadframe is overmolded with an artificial resin by a transfer molding process. The artificial resin compound forms the package of the light-emitting diode light source.
Optical components frequently display material degradation when they are located in the beam path of radiation-emitting electronic components, for example light-emitting diodes (LEDs) that emit in the ultraviolet or blue spectral region. Such material degradation, caused by the effect of high-energy ultraviolet or blue radiation, causes such optical components to exhibit a limited lifetime, the lifetime being defined as the time after which the intensity of the radiation transmitted through the optical component has declined to half its initial value. Material degradation can manifest itself for example in discoloration, in particular yellowing or browning, as well as in embrittlement and cracking of the regions of the optical component that are located in the beam path of the radiation-emitting electronic component. Elevated temperature and/or the additional action of humidity can further speed up material degradation. The lifetime of optical components is additionally reduced as a consequence of continuing technical development of LED semiconductor materials in the sense of increased radiant power of LED semiconductor materials.
Transparent thermoplastics, resins or glass have heretofore been employed in the production of radiation-emitting components and optical components, respectively.
Thermoplastics are distinguished by economy and simplicity of processing. They exhibit low radiation stability for short-wavelength radiation, however, and have a limited service temperature.
Thermosets, in contrast, are distinguished by relatively high temperature stability and good molding qualities as well as dimensional accuracy. Thermosets, however, likewise have low radiation stability for short-wavelength radiation. Their processing is costly, and material costs are comparatively high.
Glass is distinguished by good aging stability and good temperature stability, but the material costs and processing costs are high.
The use of silicone resins has been possible heretofore only to a limited degree. While silicone resins are stable against radiation and aging, the shaping processes (injection molding and molding) for silicone resins are comparatively time- and cost-intensive. Components produced by previously known methods exhibit too little dimensional stability for practical use.